Air-laid web with high modulus fibers

ABSTRACT

The present invention is directed to an air-laid composition comprising absorbent, binder, and synthetic fibers, wherein the synthetic fibers have a modulus greater than about 2 grams per denier, and a percent crimp of less than about 30%. The absorbent comprises about 40 to 80% of the weight of the composition. The binder comprises about 3-15% of the weight of the composition. The synthetic fibers comprise about 10-50% of the weight of the composition. The binder is selected from the class comprising conventional latex systems, hot melt adhesive, or binder fibers, or a mixture of these. The absorbent comprises natural absorbents or super absorbent polymer, or a combination of these. The natural absorbent materials are selected from the class consisting of wood pulp fluff, cotton, cotton linters, and regenerated cellulose fibers. The super absorbent polymer is selected from the class of agar, pectin, guar gum and synthetic hydrogel polymers. The synthetic fibers are selected from the class of polyolefins, such polyethylene, polypropylene and the like; polyesters such as polyethylene terephthalate and the like; polyamides such as nylon 6, nylon 6,6, and the like; acrylics; as well as mixtures and copolymers thereof. The synthetic fibers have an average length of from about 3-18 mm.

BACKGROUND OF THE INVENTION

[0001] 1) Field of the Invention

[0002] The present invention relates to an air-laid composition usefulin diapers, incontinence pads, sanitary napkins and other absorbent padsneeded for body fluids; filters (air filters, liquid filters); andfabrics for window treatments, upholstery, pillows and bedding. Inparticular, the present invention comprises an air-laid web compositionof absorbent, binder, and high modulus fibers that has an improved loft,compression resistance, and an increased capacity through the forminghead of the air-laid apparatus. The modulus of the fibers is greaterthan about 2 grams per denier and has a percent crimp of less than about30%.

[0003] 2) Prior Art

[0004] Disposable absorbent articles such as disposable diapers, havefound much success in the marketplace, however, there is always a needto improve these products in terms of their low density, high loft, andcompression resistance. Prior to the present invention it was known toform existing air-laid composites from natural absorbents (andoptionally up to 25% super absorbent polymers, SAP), bicomponent fibersas binder, and short cut synthetic fibers for loft and compressionresistance. This existing composition contained approximately 10%bicomponent fibers, about 10% regular polyester fibers, andapproximately 80% absorbent. This product had adequate loft, fluidintake rate and good wet strength. Generally this product was created bymixing a natural absorbent (wood pulp), and optionally the SAP, with thebicomponent fibers and the synthetic fibers and blending this mixtureand ejecting the composition through forming heads of the air-laidequipment. The composite was then introduced into a heating zone, suchthat the lower melting material of the bicomponent fiber would melt andwould run to the intersection where the fibers cross one another. Next,the composite was introduced into a cooling zone where the web wascooled, thus solidifying the molten lower melting material, therebybinding the mixture into a unitary web structure.

[0005] In this existing composition, the purpose of the naturalabsorbent such as the wood pulp and/or SAP is to absorb the body fluids,while the purpose of the bicomponent fiber is to bind the entire webtogether, and the purpose of the synthetic fibers, including the highermelting synthetic fiber component of the bicomponent fibers, is toprovide loft and compression resistance so that the maximum surface ofeach individual natural absorbent fiber/particle may be exposed to thebodily fluids.

[0006] As the industry seeks to increase capacity with the existingequipment, a problem has arisen in that the forming heads of theair-laid apparatus often clog with the current composition as thethroughput is increased.

[0007] It is an object of the present invention to improve thecomposition so as to increase the capacity without clogging of theair-laid equipment forming heads.

SUMMARY OF THE INVENTION

[0008] The present invention relates to the use of short cut fibers,which have a higher modulus than previously used synthetic polymerfibers. Employing a modification of the conventional formulation ofabout 3-15% by weight binder fiber, about 40-80% by weight absorbents,such as wood pulp fluff, and 10-50% by weight of the synthetic fiberhaving a higher modulus and lower percent crimp than conventionallyemployed fibers, permits an increase in through-put of the forming headof the air-laid apparatus.

[0009] The increase in modulus means that the fiber is stiffer. Prior tothe present invention, it was generally thought that a flexible fiberwas necessary to obtain good throughput in the forming head.

[0010] In the broadest sense, the present invention comprises anair-laid composition having absorbent, binder, and synthetic fibershaving a high modulus and low percent crimp.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The webs of the present invention are useful in diapers,incontinence pads, sanitary napkins, and other absorbent pads needed forbody fluids, filters (air filters, liquid filters); and fabrics forwindow treatments, upholstery, pillows and bedding. In particular, thepresent invention comprises a composition comprising absorbents, such aswood pulp or synthetic absorbent polymers, binder, and high modulussynthetic fibers.

[0012] The synthetic fibers in prior art processes were short cut inlength between 3 and 18 millimeters and preferably about 6 millimetersin length. Typically such fibers have a modulus of approximately 1.5grams per denier (gpd) or less. With the present invention, the fibersemployed are heat set longer such that the modulus is greater than about2 gpd and preferably greater than about 2.5 gpd. The increased moduluscauses the overall fiber to be stiffer and contrary to popular belief,it actually exits the forming head of air-laid apparatus much cleanerwithout clogging and blocking the forming head compared withconventional compositions. The fibers of the present invention also havea low percent crimp, and particularly less than about 30%. These fiberswill have a preferred range of 4 to 8 mm in length and a denier of about1.5 to 4, and preferably a denier of about 3. The weight of the webs ofthe present composition range from about 50 to 500 grams per squaremeter (gsm).

[0013] Suitable absorbents are natural absorbents or syntheticabsorbents primarily know as super absorbent polymers, or a mixture ofthese. The absorbents comprise 40-80% by weight of the web. Naturalabsorbents are hydrophilic materials such as cellulosic fibers, woodpulp fluff, cotton, cotton linters, and regenerated cellulose fiberssuch as rayon, or a mixture of these. Preferred is wood pulp fluff,which is both inexpensive and readily available.

[0014] While conventional wood pulp fibers are readily absorbent,compacted wood pulp fibers do not absorb as much bodily fluid as when aportion of the wood pulp fibers has been replaced with synthetic fibers,and preferably polyester fibers, which provide loft to the composite.Providing loft to the composite exposes more surface area of the woodpulp fibers to the bodily fluids and thus the wood pulp fibers are muchmore efficient in absorbing the bodily fluid.

[0015] Absorbent pads employing natural absorbents may not provideadequate fluid intake for all circumstances. Also natural absorbents arevery bulky. Accordingly, many absorbent pads employ SAP in relativelylow quantities. This is because the cost of SAP is much higher than thecost of natural absorbents. Replacing some of the natural absorbentswith SAP can reduce the overall bulk of the pad and/or provide superiorfluid intake.

[0016] As used herein, the term “super-absorbent polymer” or “SAP”refers to a water-swellable, generally water-insoluble material capableof absorbing at least about 10, desirably about 20, and preferably about50 times or more its weight in water. The super-absorbent polymer may beformed from organic material, which may include natural materials suchas agar, pectin, and guar gum, as well as synthetic materials such assynthetic hydrogel polymers. Synthetic hydrogel polymers include, forexample, carboxymethyl cellulose, alkali metal salts of polyacrylicacid, polyacrylamides, polyvinyl alcohol, ethylene maleic anhydridecopolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinylmorpholinone, polymers and copolymers of vinyl sulfonic acid,polyacrylates, polyacrylamides, polyvinyl pyridine, and the like. Othersuitable polymers include hydrolyzed acrylonitrile grafted starch,acrylic acid grafted starch, and isobutylene maleic anhydride copolymersand mixtures thereof. The hydrogel polymers are preferably lightlycrosslinked to render the materials substantially water insoluble.Crosslinking may, for example, be by irradiation or covalent, ionic, vander Waals, or hydrogen bonding. Suitable materials are available fromvarious commercial vendors such as the Dow Chemical Company, AlliedColloid, Inc., and Stockhausen, Inc. The SAP may be in the form ofparticles, flakes, fibers, rods, films or any of a number of geometricforms.

[0017] The high modulus, low percent crimp synthetic fibers may beformed from any polymeric material capable of forming fibers that can beformed into a fibrous web. Suitable polymeric material, from which thesynthetic fibers may be formed, include polyolefins, such aspolyethylene, polypropylene, and the like; polyesters such aspolyethylene terephthalate or polybutylene terephthalate, orcopolyesters such as polyethylene terephthalate-isophthalate orpolyethylene terephthalate-adipate and the like; polyamides such asnylon 6, nylon 6,6, poly(iminocarboxylpentamethylene) and the like;acrylics; as well as mixtures and copolymers thereof. Preferred ispolyester fiber such as polyethylene terephthalate. The synthetic fibersmust have a modulus of greater than about 2.0 gpd, and preferablygreater than about 2.5 gpd, and most preferably greater than about 3.0gpd. The synthetic fibers must also have a low percent crimp, preferablyless than about 30%, and more preferably less than about 25%.

[0018] The binder of the present invention can be based on conventionallatex systems, hot melt adhesives, or binder fibers, or a mixture ofthese. Conventional latex systems such as styrene-butadiene copolymer,acrylate, and polyvinyl acetate systems, as well as mixtures of theseare well known. Hot melt adhesives are generally solid powder materialsor non-latex paste and liquid compositions well known to those in theart. Binder fibers can be conventional low melt fibers or bicomponentfibers. Conventional low melt fibers can be polyolefins, for example,and in particular can be linear low density polyethylene. Bicomponentfibers having a denier of between 2 and 6 are the preferred binderfiber. Bicomponent fibers can be of the type in which the low meltingpoint portion is adjacent to the high melting point portion such as aside-by-side configuration, or in a sheath-core configuration whereinthe sheath is the lower melting component and the core is the highermelting component. The binders are thermally bonded by conventionalmeans such as by using an oven (hot air, radiant or microwave), orcalender roll(s), or by ultrasonic energy. It is contemplated that theweb of the present invention will comprise between 3 and 15% by weightbinder fiber, such as bicomponent fiber. This amount of binder fiber isdeemed to be adequate to bind the web into a unitary structure.Preferably, about 10% by weight binder fiber (based on the weight of theweb) gives most satisfactory results. When a conventional latex systemis employed with the present invention, the amount of binder may rangefrom 5-60% by weight of the web.

[0019] Suitable bicomponent fibers are polyethylene/polypropylene;polyethylene/polyester (especially polyethylene terephthalate);polypropylene/polyester; and copolyester/polyethylene terephthalate,such as polyethylene terephthalate-isophthalate/polyethyleneterephthalate; nylon 6/nylon 6,6; and nylon 6/polyethyleneterephthalate; as well as mixtures of these. Preferablypolyethylene/polyester are used, especially grafted polyethylene/polyethylene terephthalate, such as linear low densitypolyethylene/polyethylene terephthalate.

[0020] The web of the present invention comprises between 3 and 15% byweight binder fiber such as bicomponent fiber. This amount of binderfiber is deemed adequate to bind the web into a unitary structure.Preferably, about 10% by weight gives most satisfactory results.Moreover, the web also has 40 to 80% by weight absorbent, such as woodpulp fibers, some being optionally being substituted by SAP. Lastly theweb has synthetic fibers (of length between 3 and 18 mm), having adenier between 1.5 and 4, in an amount from 10% to about 50% by weight,based on the weight of the web. The weight of the webs of the presentcomposition range from about 50 to 500 grams per square meter (gsm).

[0021] The web may be formed by an air-laid process by merely mixing orblending the various fibers together and subjecting them to a flowingair stream which carries the fibers to a surface, preferably a screensurface, upon which the fibers are deposited in a very random order. Ifbinder fibers are employed, the web is then conveyed to a heated zone ofsufficient temperature and having a sufficient residence time for theweb such that the low melting material of the binder fiber melts, flowsto the intersection of a group of overlaid, contacting and intersectingfibers. Next, the web is transported on the conveyor belt to a coolingzone where all molten material solidifies thus making the webstructurally rigid. If the binder is a latex system, the web is coatedwith the latex (by spraying, dipping, etc.) and the latex is allowed todry and cure, thereby solidifying. Thereafter, the web may be cut intovarious lengths and widths for the end use applications, namely,fenestration drapes, dental bibs, eye pads, diapers, incontinent pads,sanitary napkins, wound dressing pads, air filters, liquid filters, andfabrics such as drapes, bedding or pillows.

[0022] The web can also be used in conjunction with other components,such as part of a laminate with a woven or nonwoven material or fabric.For example, spun-bond/melt-blown /spun-bond fabric (“SMS”) are knownand have many uses. Stitch-bonded fabric is another known example of amulticomponent structure comprising fabric and a fiber web sewn orstitched together.

TEST PROCEDURES

[0023] The physical properties of the synthetic fibers were measuredaccording to the following procedures.

Linear Density (Denier)

[0024] The denier of the synthetic fibers was measured according to ASTM1577-96, option A, using uncut fibers (tow).

Modulus

[0025] The modulus was measured according to ASTM 3822-96. Uncut fibers(tow) were used with a 5 inch gauge length and a strain rate of60%/minute. The modulus is reported as the load at 10% elongation ingram/denier (gpd).

Crimp Frequency (Crimps Per Inch, CPI)

[0026] The crimp frequency was measured according to ASTM 3937-94, usingoption one for preparing the sample.

Percent Crimp

[0027] A length of tow, approximately 1.25 m, is clamped at one end andtensioned to remove the crimp. The tow is cut at a distance of 1 m fromthe clamp. The tow is allowed to relax, and the length of the relaxed,crimped tow band is measured (L, cm). The percent (%) crimp is 100−L.

Forming Head Capacity

[0028] Trials were conducted on a Dan-Web airlay former. The basisweight of the web was kept constant at 263 gsm by increasing the beltspeed as the throughput of fibers through the forming head wasincreased. The maximum throughput was defined as the maximum ratewithout choking the forming head, which resulted in a decrease in webbasis weight.

EXAMPLE 1

[0029] A series of polyester fibers were produced by a conventionalpolyester process, in which the heatsetting conditions were changed tochange the modulus of the fibers. Crimping conditions were also changedto give a range of percent crimp. The crimp frequency was kept constantat 7 cpi, the denier at 3, and the tow was cut to a cut length of 6 mm.Comparative run 4 is a commercial product, KoSa T224.

[0030] A blend containing 10% of these fibers, 12% KoSa T255 bicomponentbinder fiber, and 78% wood pulp was fed to the forming head. The resultsare set forth in Table 1 below. TABLE 1 Maximum Run Fiber Modulus, gpdFiber % crimp throughput, lb./hr 1 2.85 22 55 2 2.85 30 45 Comparative 32.85 36 20 Comparative 4 1.5 22 45 Comparative 5 1.3 23 20

[0031] As Table 1 illustrates a stiffer, high modulus fiber can be runat a higher forming head throughput than conventional low modulusfibers. In addition a lower percent crimp gives higher forming headthroughput.

[0032] Thus it is apparent that it has been provided, in accordance withthe invention, a composition that fully satisfies the objects, aims, andadvantages set forth above. While the invention has been described inconjunction with specific embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended to embrace all such alternatives, modifications andvariations as fall within the spirit and board scope of the invention.

What is claimed is:
 1. An air-laid composition comprising: absorbent,binder, and synthetic fibers, said synthetic fibers having a modulusgreater than about 2 gpd; and a percent crimp less than about 30%. 2.The composition of claim 1, wherein said absorbent comprises naturalabsorbents or super absorbent polymer, or a combination of these.
 3. Thecomposition of claim 2, wherein said natural absorbent materials areselected from the class consisting of wood pulp fluff, cotton, cottonlinters, and regenerated cellulose fibers.
 4. The composition of claim2, wherein the super absorbent polymer is selected from the class ofagar, pectin, guar gum and synthetic hydrogel polymers.
 5. Thecomposition of claim 4, wherein said synthetic hydrogel polymers isselected from the class of carboxymethyl cellulose, alkali metal saltsof polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene maleicanhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose,polyvinyl morpholinone, polymers and copolymers of vinyl sulfonic acid,polyacrylates, polyacrylamides, polyvinyl pyridine, and mixtures of twoor more of these.
 6. The composition of claim 1, wherein said absorbentcomprises from about 40 to about 80% of the weight of said composition.7. The composition of claim 1, wherein said synthetic fibers areselected from the class of polyolefins, such polyethylene, polypropyleneand the like; polyesters such as polyethylene terephthalate and thelike; polyamides such as nylon 6, nylon 6,6, and the like; acrylics; aswell as mixtures and copolymers thereof.
 8. The composition of claim 1,wherein said synthetic fibers comprise from about 10 to about 50% byweight of said composition.
 9. The composition of claim 1, wherein saidsynthetic fiber has a denier of between about 3 to about
 15. 10. Thecomposition of claim 1, wherein said binder is selected from the classcomprising conventional latex systems, hot melt adhesive, or binderfibers, or a mixture of these.
 11. The composition of claim 10, whereinsaid binder is binder fibers and comprises 3-15% by weight of saidcomposition.
 12. The composition of claim 10, wherein said binder is aconventional latex system comprising styrene-butadiene copolymer,acrylate polymer, and polyvinyl acetate polymer, and mixtures of these.13. The composition of claim 11, wherein said binder fibers arebicomponent fibers selected from the class ofpolyethylene/polypropylene; polyethylene/polyester;polypropylene/polyester; copolyester/polyethylene terephthalate; andmixtures of these.
 14. The composition of claim 1, wherein said modulusis greater than about 2.5 gpd.
 15. The composition of claim 1, whereinsaid percent crimp is less than about 25%.
 16. The composition of claim1, wherein said synthetic fibers have a denier in a range from about 3to about
 15. 17. The composition of claim 1, wherein said syntheticfibers have an average length of from about 3-18 mm.
 18. The compositionof claim 1, wherein said modulus is greater than about 3.0 gpd.
 19. Arigid air-laid web comprising: 10-50% by weight polyester fiber, 3-15%by weight binder fiber, and 40-80% by weight absorbent, said polyesterfiber having a modulus greater than about 2 gpd and a percent crimp ofless than about 30%.
 20. The web of claim 19, wherein said polyesterfiber has a modulus greater than about 2.5 gpd and a percent crimp lessthan about 25%.
 21. A process of forming a rigid air-laid webcomprising: blending 10-50% by weight polyester fiber, 3-15% by weightbicomponent fibers, and 40-80% by weight wood pulp together andsubjecting them to a flowing air stream; heating said web until saidbicomponent fibers become molten; and cooling said web until said web isrigid, wherein said polyester fiber has a modulus of greater than about2 gpd, and a percent crimp of less than about 30%.